Description

On 8 October 2019, a BAe Jetstream 32 (PH-RCI) being operated by AIS Airlines on a scheduled domestic passenger flight from Münster/Osnabrück to Stuttgart as W2-6505 which was being used for line training made a rejected takeoff from significantly above the applicable V1 in day VMC after it was impossible to rotate the aircraft. An excursion off the side of the runway then occurred and another aircraft waiting at a holding point was just avoided before the runway was regained. Damage to the aircraft and to ground lighting/signage was relatively minor and there were no injuries to the three crew or the only passenger.

Investigation

An Investigation was carried out by the German Federal Bureau of Accident Investigation (BFU). The CVR and FDR were both removed from the aircraft and their relevant data were successfully downloaded.

It was noted that the 63 year-old Captain held a Dutch licence which included a limitation that it was valid only when with or as a copilot. He had a total 8,860 hours flying experience of which 767 hours were on type but most of the remainder had been obtained during light aircraft training flights as a flying instructor. The 26 year-old First Officer held a French licence issued in February 2019 and was a French national with a licence endorsement for level 5 English. He had a total of 157 hours flying experience of which just 47 minutes were on type, obtained during early July 2019 whilst undergoing training for a Jetstream 32 type rating which had otherwise all been conducted in a full flight simulator. Over three months had elapsed since his only previous flight in the aircraft type.

What Happened

The flight was scheduled to depart at 1730 LT and both pilots arrived at the airport ahead of the rostered 75 minute report time for a training flight. After about half an hour, during which the First Officer had reviewed and, as necessary, filed the flight documentation, the crew went to the aircraft. After the Captain had conducted the external check, the crew then completed the flight deck pre-flight checks together. They were informed that the allocated CTOT for the flight which was not until 31 minutes after the STD and according to the Captain’s statement “he was angry about the delayed departure time” and was recorded telling the GND controller that he was “displeased” at the delay. At STD, the GND controller offered to send a “ready message” which can sometimes lead to an improvement in the initially-issued CTOT.

According to the statements of the GND and TWR controllers, “it became clear from the radio communication that the crew was not familiar with the meaning of "ready message". With 20 minutes to go until the issued CTOT, the GND controller approved engine start at the crew’s discretion to meet it but when it had not occurred with 9 minutes to go, he again issued it. With less than 3 minutes to go, the flight subsequently requested and received taxi clearance via taxiways ‘D’ and ‘A’ to the holding point for runway 25 (see the illustration below). It was noted that according to the First Officer’s statement, during the taxi out he had already felt “a bit lost (and) behind the aircraft and had attributed this to the fact that he had not flown the aircraft type for three months”. As the aircraft was only fitted with a nose gear steering tiller at the left seat position, the First Officer was initially acting as PM and so he actioned the instruction to change from GND to TWR as the aircraft approached the holding point.

The airport layout showing the subsequent takeoff attempt and rejection with runway excursion. [Reproduced from the Official Report]

Takeoff clearance followed at 30 seconds after the CTOT and the First Officer began to complete the line-up checklist. The CVR data showed that in doing so, he had missed out item 4 which was the full and free movement check of the flying controls. The next item on the checklist was to test and select on the Stall Protection System but he had difficulty in immediately locating the switch positions which the Captain noticed and said “leave it, not so important” and so this item was skipped.

Takeoff from the 2170 metre-long runway was commenced 1½ minutes after the clearance had been issued. Although the First Officer was going to take over as PF once directional control by rudder was possible, the Captain initially controlled the aircraft direction using the nose wheel steering system, and transferred control to the First Officer at around 70 KIAS. At the calculated V1 of 108 knots, he called “V1 rotate” but when the First Officer attempted to do so, he found that the control column could not be moved and announced this accordingly as the aircraft continued straight ahead and seven seconds after the V1 call, a rejected takeoff was commenced at a speed of approximately 130 KIAS.

FDR data was found to show that from the time the V1 call was made, the aircraft heading began to deviate to the right of the centreline, reaching a recorded maximum of +11° within 5 seconds which was about the time the takeoff was rejected. The heading then began to decrease over the next 11 seconds by a total of 21° and on regaining the runway, the heading then increased again as the aircraft was realigned with the runway heading. These changes corresponded to a deviation off the north side of the 45 metre-wide runway which reached a maximum of 23 metres from its edge before the return onto it began. During the excursion, the aircraft was on unpaved ground for a distance of 530 metres and passed, at a speed of “approximately 119 KIAS”, in front of a ROBIN DR-400 Cadet single engine light aircraft (see its position on the illustration above) which was waiting at the holding point on the taxiway from the north side of the airport.

Once back on the runway, the TWR controller asked the reason for the rejected takeoff and the Captain stated that it was because the (control) gust lock was still engaged. The aircraft was taxied clear at the end of the runway and returned to the apron where it was found that damage to the aircraft was minor and limited to one propeller blade, the left main landing gear tyre and a small area of the lower fuselage cargo compartment. An inspection of the runway and the excursion area found one damaged edge light and impact damage to an information sign near to the taxiway on which the DR400 had been waiting. Fuel leakage was also observed in the vicinity of the left and right main landing gear attachment to the wing structure. The absence of significant damage to the aircraft as a result of the excursion was due to the relatively level, dry and unobstructed surface traversed during it (see the illustration below).

The main gear marks looking back from the point where the runway was regained. [Reproduced from the Official Report]

The Gust Lock Problem

A gust lock system is provided to prevent movement and potentially resultant damage to the primary flight control surfaces and in the case of the Jetstream 32 was controlled via a single lever located on the right hand side of the centre pedestal as illustrated below.

The Gust Lock Lever shown in the controls locked position as during the takeoff. [Reproduced from the Official Report]

According to the Captain, after the rejected takeoff the lever was found to be in the locked position which by design should have meant that it was mechanically impossible for both power levers to be move simultaneously above the flight idle position. An examination of the mechanism found that this had been possible because a fork-ended control rod was bent instead of being straight (see the lustration below). It was noted that this system had last been inspected during a routine check seven months earlier with no recorded findings of any control rod distortion.

Bent control rod as found (highlighted). Reproduced from the Official Report

Straight control rod as installed. [Reproduced from the Official Report]

The Captain’s Performance

His evident failure to operate in accordance with SOPs not only hazarded safe flight but provided an appallingly inappropriate example to an extremely inexperienced trainee pilot and did so on a public transport flight. In respect of his training role and in particular the complete lack of continuity in the First Officer’s type training for his first experience as a professional transport pilot, he completely failed to ensure an unhurried departure despite the ATC offer of engine start 20 minutes before takeoff time. It was also evident from the unfamiliarity with the long established ATC CTOT system in Europe that having gained most of his flying experience as a light aircraft instructor, he lacked sufficient understanding of the way the commercial air transport system operated.

The Operator’s Procedures and Practices

When a comparison was made between the operator’s checklists in their OM and the master checklists in the Manufacturers Operating Manual (MOM), some significant discrepancies were found. These included the MOM checklist item of ‘GUST LOCK … RELEASE / FULLY DOWN’ being absent from the operator’s taxi and line up checks altogether and the item ‘FLYING CONTROLS … FULL and FREE’ being shortened to ‘Flight Controls … CHECKED’ and included in the operator’s line up checks instead of in the taxi checks as in the MOM. The BFU concluded that these differences were “not acceptable” in safety terms.

As a result of its wider findings during the Investigation, “the BFU was of the opinion that it is probable that other flight crew did not check the proper function of the Gust Lock system during pre-flight preparation or flight deck checks and that the technical deficiency had existed for some time”. The Captain’s attitude to compliance with operational procedures therefore had to be seen in that context.

The Design of the Gust Lock System

Under the aircraft type certification provisions in CS25 for large aeroplanes, it was noted that a gust lock system which prevents normal operation of the control surfaces must either automatically disengage when a pilot operates the primary flight controls in a normal manner or limit the operation of the aeroplane and provide the pilot with an unmistakable warning at the start of take-off. It must be designed in such a way that it cannot become inadvertently engaged in flight.

Shortly after the introduction of the Jetstream 32 (in 1988), the manufacture became aware of three instances, two of which led to a lateral runway excursion like the one in the event under investigation, involving the very similar Jetstream 31 due to the Gust Lock system not being fully disengaged and the flight crew not checking full and free movement of the flight controls. After the first of these, the Crew Manual was amended to stress the absolute necessity of checking free movement of all control surfaces after disengaging the Gust Lock system.

When four reports of it being possible to move both power levers simultaneously beyond the flight idle position despite the gust lock system being engaged, two of which occurred on Jetstream 32 aircraft, a 1992 SB provided for a reinforced version of the control rod bent in the event under investigation and in May 1994, the status of this SB was changed from ‘Optional’ to ‘Highly Recommended’ and the new rod was fitted at build. The aircraft involved in the event under investigation was manufactured in 1989 and it was found that this ‘Highly Recommended’ SB had not been implemented.

The Investigation observed that although the problem has been “known for decades”, takeoff attempts with gust lock systems engaged continue to occur on a range of aircraft types with sometimes potentially fatal consequences such as in a 2014 accident in the USA. It noted the frequently repeated need for “compliance with and adherence to procedures and checklists and mutual monitoring as part of flight-safety-improving CRM". It also observed that “maintenance personnel need to understand the importance of a fully functional gust lock system which prevents takeoff when in the engaged position and check its proper function regularly”. However, it recognised that “ultimately, only a complete check of flight controls prior to a takeoff can ensure that all flight controls are full and free”.

The Cause of the Serious Incident was formally documented as “veering off the runway during takeoff due to the engaged gust lock system which locked the control surfaces and resulted in the pilots temporarily losing control of the aircraft”.

Seven Contributory Factors were also identified as:

• Insufficient supervision, support and monitoring of the Line Training Captain.
• Inexperience of the young co-pilot and a long gap between his obtaining a type rating and his first commercial scheduled flight.
• Insufficient Crew Resource Management of the flight crew.
• Pressure of time created by the crew between engine start-up and take-off.
• Non-stringent application and erroneous completion of the checklists.
• Checklist items, procedures and choice of wording in the checklists of the operator which did not completely correspond with the ones of the aircraft manufacturer
• A mechanical deficiency in the gust lock system, which allowed the engine power of both engines to be increased simultaneously.

Safety Action taken by the aircraft operator as a result of the event was noted as adding the item “Gust Lock Handle … Full Down and Flight Controls … Full Free” to the Line Up checklist.

One Safety Recommendation was made based on the findings of the Investigation as follows:

• that the European Union Aviation Safety Agency (EASA) should convert the ‘Highly Recommended’ Service Bulletin (SB) 27JM-5350 ‘Modified Push Rod Assembly at Gust Lock / Power Lever Baulk Mechanism’ into a mandatory Airworthiness Directive in order to safeguard the function and prevent take-offs with engaged Gust Lock for all Jetstream 31/31 aircraft.

The Final Report of the Investigation was completed on 24 November 2020 and published during February 2021.

Related Articles

• Runway Excursion
• Flight Control Locks
• Checklists - Purpose and Use
• Crew Resource Management (CRM)
• GLF4, Bedford MA USA, 2014
• Service Bulletin (SB)
• Airworthiness Directive